Complete refactoring for rktplayer, in order to make it play on DLNA renderers and also use UpNP media server resources.

library/base/media-container.rkt

@@ -0,0 +1,52 @@
+#lang racket/base
+
+(require racket/class
+         "media-item.rkt")
+
+(provide media-container%)
+
+;; A media container contains media-item% instances. An item can itself be
+;; another media-container%, or it can be a track<%>.
+(define media-container%
+  (class media-item%
+    (init [id #f])
+
+    (super-new
+     [id id]
+     [kind 'container])
+
+    (abstract
+     get-title
+     get-items
+     get-track-reliver)))
+
+(module+ test
+  (require rackunit)
+
+  (define track-reliver
+    (lambda (track-factory-id track-relive-info)
+      (list track-factory-id track-relive-info)))
+
+  (define test-container%
+    (class media-container%
+      (super-new [id 'container-id])
+
+      (define/override (get-title)
+        "Container")
+
+      (define/override (get-items)
+        '())
+
+      (define/override (get-track-reliver)
+        track-reliver)))
+
+  (define container
+    (new test-container%))
+
+  (check-equal? (send container get-id) 'container-id)
+  (check-equal? (send container get-kind) 'container)
+  (check-eq? (send container get-container) container)
+  (check-false (send container get-track))
+  (check-equal? (send container get-title) "Container")
+  (check-equal? (send container get-items) '())
+  (check-eq? (send container get-track-reliver) track-reliver))